>> well, public events like this are absolutely the hardest thing to provide a very secure environment. you literally can't do it. if your standard is nobody can be at risk at a large public event, we're never going to have another u 2 concert. there are basic procedures for events like this. they're well established. we've learned from everything from the '96 olympic bombings to what you should do. are this they going to do a review? did we do the due diligence? they'll have to. it will be pretty clear whether that was done or not. and then we'll move on from there and we may learn some things to improve. we've got a pittsburgh marathon coming up, other things. you can't stop these public events. you can't make them perfectly secure, but you can do due diligence. the key point is the best way to stop these attacks is good intelligence, good police enforcement that goes out and finds the perpetrators before they do something. >> you can't protect every inch of a 26.2 mile race of course, that's for sure. james carafano, security expert in washington. thank you so much for being with us